1. Field of the Invention
The present invention relates in general to radar, and in particular to system for simulating a target for pulse Doppler radar that employs Digital Signal Processing.
2. Description of the Prior Art
There are a number of devices for testing and calibrating radars. Such devices are generally known as target simulators. The following references are a sample of teachings related to target simulation.
The patent of Sommers et al., U.S. Pat. No. 3,331,070, discloses a moving target simulator for Moving Target Indicator (MTI) radar. The simulator receives successive pulses from the radar and reflects back the successive pulses while phase-shifting in time each of the reflected successive pulses 180 degrees from the preceding one.
The patent of Eddy, U.S. Pat. No. 4,686,534, discloses a target simulator for a pulse compression radar. The simulator receives a signal from the radar and adds to the signal modulation components which are in both phase or frequency domain and in amplitude domain. The signal is then returned to the radar.
The patent of Warren, U.S. Pat. No. 4,319,247, discloses a target simulator for radar. The simulator samples radar-transmitted pulses and imposes successive delays on the sample. The simulator then retransmits the delayed pulses to the radar. The simulator includes a frequency shifter which simulates Doppler shift. The Warren patent also discloses the returning of the radar-transmitted pulses with pulses that are of successively different amplitude.
The Adams et al., U.S. Pat. No. 3,329,953, discloses a Doppler target simulator which uses a bidirectional phase-shifter controlled by a Doppler signature driver circuit to vary the phase of a returned signal.
These systems do not address the issue of antenna size, the signal-to-noise and the phase-drift problems which are present when a small antenna is used with a simulator. There is a need for a system which does adequately address these problems.